As an evolutionary standard of IEEE802.16e, IEEE 802.16m targets for doubling average user throughput, cell edge user throughput compared to IEEE802.16e in downlinks (DLs). These targets are very challenging to reach due to severe inter-cell interference at low frequency reuse scenarios. New techniques are highly desirable to achieve these goals.
Multi-User MIMO (MU-MIMO) is a Space Division Multiplexing Access (SDMA) technique efficient for capacity enhancement, with a single Base Station (BS) transmitting multiple data streams to multiple mobile stations (or users) over the same time-frequency resources through precoding techniques. Thanks for the precoding techniques, each mobile station makes no or small interference to other users.
Macro-Diversity HandOver (MDHO) technique based on Single User MIMO (SU-MIMO) scheme has been standardized in IEEE 802.16e. In this technique, when a mobile station locates in one MDHO zone, multiple base stations which serve this MDHO zone send same downlink signals to the mobile station over the same time-frequency resource. The system capacity in the MDHO zone is quite low due to that the multiple base stations use the same time-frequency resource to serve only one same mobile station.